The ship wherein Theseus and the youth of Athens returned from Crete had thirty oars, and was preserved by the Athenians for many centuries. To ensure it was well-maintained, they replaced the old planks as they decayed, putting in new and stronger timber in their places. And so they did replace the oars, and the rope, and the sails, as needed.
In time, every part of the ship had been replaced. This brought about a great philosophic debate, as one side held that as it had always been the Ship of Theseus, and as changing one plank did not make it less so, it remained the Ship of Theseus now even though a single plank has been replaced so often that none were original. Whereas the other side held that since no part of the ship was original, and indeed all the replaced parts could have been gathered and used to build a second, older ship, that clearly what was left was no longer the ship of Theseus.
Then Poseidon Released the Kraken, and killed them all.